In space startup method for nuclear fusion rocket engines

ABSTRACT

The invention is for a startup system for nuclear fusion engines in space. The combustion of hydrogen and oxygen produces heat that is used by a heat engine to produce electricity. This can be supplemented by electricity from other operating engines. The exhaust from the combustion is condensed and electrolyzed to produce hydrogen and oxygen once the engine is in operation. This provides a constant source of energy for future startups. The engine is started up at partial power in electricity generation mode and this power replaces the power from the combustion as it grows. The combustor uses the same heat engine as the nuclear engine uses for power generation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 61/868,629 filed Aug. 22, 2013. The disclosure of this applicationis incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under grant no.DE-AC02-09CH11466 awarded by the Department of Energy. The governmenthas certain rights in this invention.

FIELD OF THE INVENTION

The present invention generally relates to the startup or restart ofnuclear fusion engines in space.

BACKGROUND OF THE INVENTION

Nuclear fusion engines will be needed to power the next generation ofrobotic spacecraft and future human missions to Mars.

Starting up a fusion reaction requires considerable power for a shortperiod of time. The power is used to heat the reactants to fusiontemperatures until the reaction is self-sustaining. It also energizesthe superconducting coils used to confine the plasma and powersauxiliary equipment.

The source of the startup power is a major concern for nuclear fusionengines. It must be reliable and available at all times. It may have tolast for several years without being used.

Terrestrial fusion reactors use electric power from the grid to starttheir reactions. Without a source of external power a space fusionengine would need to be so reliable that it would never shutdown unlessit were near an orbiting power station.

Yurash (U.S. Patent Application Publication No. 2009/0000268) disclosesa fusion rocket requiring an alpha particle source to start the reactionbut does not disclose a method to power the alpha particle source.

Flood (U.S. Patent Application Publication No. 2010/0264656) disclosesan orbital solar station that could be used to start up a fusionreactor. Orbiting power stations would require large solar arrays andlarge power storage that could deliver high power in short bursts. Thelargest solar power system to date, on the International Space Station,would be too small to start proposed fusion engines. Even if suchstations could be built, they would need to be located in orbits, suchas around Mars, where spacecraft were likely to go. If the fusion enginewere not operational, a separate space tug would be required to bringthe power station and this would greatly limit the applicability of thefusion engine technology.

Williams, et al (Realizing “2001: A Space Odyssey”: Piloted SphericalTorus Nuclear Fusion Engine”, NASA/TM-2005-213559) discloses an onboardfission reactor for fusion reactor startup. This has the disadvantage ofbeing heavy and dangerous due to the presence of highly radioactivematerial. For example, in the event of a catastrophic accident, thespacecraft may to reenter the Earth's atmosphere, spreading radioactivematerial over a broad area. The safety problems associated with fissionreactors have prevented the widespread use of fission reactors inspacecraft.

There are numerous energy storage options that can be considered.Weinberger (U.S. Pat. No. 5,214,981) discloses a superconducting magnetbearing flywheel for energy storage. This system is an alternative tothe system disclosed in this application. Its advantage over otherflywheel system is that the electromagnetic bearings are superconductingand do not require power which limit the time other systems can storepower. Nonetheless, it would still require that this, an active system,be kept operating for long periods of time. In addition, the largeflywheels present an operational safety hazard. It is also not clearthat the power to mass ratio is suitable for this application.

Fuel cells are known devices that could provide power for startup. VonDoehren (U.S. Pat. No. 3,546,019) discloses fuel cells for use as abattery. Fuel cells were used extensively in the Apollo program forelectricity generation. Pettigrew (U.S. Pat. No. 5,733,421) discloses ahydrogen oxygen fuel cell. A fuel cell converts the chemical reactioninto electricity directly. Fuel cells do not have the high rates ofdischarge required. Fuel cells could be an element of the fusion reactorstart up system but by themselves are insufficient.

Batteries are a well-known electricity storage technology. Batteries,however, have very low energy densities. For example, a Cobalt LithiumIon has an energy density of 0.875 MJ/kg. This is much too low for afusion reactor startup. In contrast, hydrogen fuel contains 142 MJ/kg.In addition, batteries cannot discharge fast enough for thisapplication.

Batteries or fuel cells could be supplemented by supercapacitors orsupercapacitors to attain the high discharge rates. Martienssen (U.S.Patent Application Publication No. 2012/0187906) discloses the use ofsupercapacitors for automobiles with batteries or fuel cells. Thisreduces the wear and tear on batteries and enables both fuel cells andbatteries to deliver high power. However, the energy density ofsupercapacitors is very low, 0.018 MJ/kg, and the startup system wouldrequire a large bank of supercapacitors to meet the power requirements.

Electrolysis is a well-known process for breaking water into hydrogenand oxygen. Hackmyer (U.S. Pat. No. 4,265,721, May 5, 1981) discloses anovel system using microwave energy. Such systems could be used torecover fuel for future engine startups but by themself do not comprisea solution to the problem.

If the spacecraft has multiple fusion engines that can produce powerthen the other engines can provide the startup power. However, this doesnot solve the problem of a situation in which all of the engines shutdown.

SUMMARY OF THE INVENTION

The present invention provides a method for starting up nuclear fusionengines in space and restarting engines that have shut down. Therefore,our invention has the following objects and advantages: to providestartup up power for a nuclear fusion rocket engine; to provide aconstant source of fuel for the startup process to allow for unlimitedstartups; to use existing heat engines and power generators built intothe fusion engine so as to minimize the mass of the system.

Deuterium can be used interchangeably with hydrogen in this invention.Deuterium is used as fuel for a fusion engine and it may be advantageousto use it for startup as well. However, common hydrogen, or protium, maybe used.

The combustion of hydrogen and oxygen produces heat that is used by aheat engine to produce electricity. This can be supplemented byelectricity from other operating engines if they are available. 1 kgHydrogen produces 142 MJ/kg of energy when combusted with 8 kg ofoxygen.

The exhaust from the combustion is condensed and electrolyzed to producehydrogen and oxygen once the engine is in operation. This provides aconstant source of fuel for future startups.

The engine is started up at partial power in electricity generation modeand this power replaces the power from the combustion as the enginesreturn to full power.

The combustor uses the same heat engine as the nuclear fusion engineuses for power generation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of the system;

FIG. 2 is a flow diagram showing system operation.

DETAILED DESCRIPTION

In the following description, for purposes of explanation, specificnumbers, materials and configurations are set forth in order to providea thorough understanding of the invention. It will be apparent, however,to one having ordinary skill in the art, that the invention may bepracticed without these specific details. In some instances, well-knownfeatures may be omitted or simplified so as not to obscure the presentinvention. Furthermore, reference in the specification to “oneembodiment” or “an embodiment” means that a particular feature,structure or characteristic described in connection with the embodimentis included in at least one embodiment of the invention. The appearancesof the phrase “in an embodiment” in various places in the specificationare not necessarily all referring to the same embodiment.

The present invention advantageously provides a method for starting upnuclear fusion rocket engines in space.

During the course of this description like numbers will be used toidentify like elements according to the different views, whichillustrate the invention.

An embodiment of the invention is shown in FIG. 1. This diagram showsthe system operation. FIG. 2 shows a flowchart for the startupprocedure.

Referring to FIG. 1, liquid hydrogen, for example, may be stored in acryogenic fuel tank 12. This would be similar to the fuel tanks used forthe nuclear fusion engine fuel. Liquid oxygen, for example, may bestored in a cryogenic fuel tank 14. The oxygen and hydrogen are combinedin a combustion chamber which produces hot exhaust gases 16, i.e. watervapor. Less than 1 kg of deuterium and/or hydrogen is needed to startreactors ranging between 1 to 20 MW.

The exhaust gases 16 flow to a heat exchanger 20. The heat exchanger 20removes most of the heat from the exhaust gas 16. The heat flows to aheat engine 32 that converts the heat energy to electricity for use instarting up a fusion engine heating system 24.

An electrolysis unit converts the water into hydrogen and oxygen, 22.Electrolysis is the process by which a non-spontaneous reaction isforced to occur using a direct current. In order for electrolysis tooccur, a specific apparatus must be assembled. This apparatus mustinclude a container, a power source, and conductors that allowelectricity to flow from the power source to the substance that is inthe container. Each conductor will function as either an anode or acathode when the direct current is present. At the negatively chargedcathode, a reduction reaction takes place in which electrons from thepower source are given to positively charged hydrogen cations such thatH₂ gas is formed.2H+(aq)+2e−→H₂(g)  (Equation 1)

At the positively charged anode, an oxidation reaction occurs in whichO₂ gas is formed and electrons flow to the anode to complete thecircuit.2H₂O (l)→O₂(g)+4H+(aq)+4e−  (Equation 2)

Ideally, the amount of hydrogen generated is twice the number of molesof oxygen, however this is rarely the case. The fusion heating system 24requires electric power to operate. In an embodiment, fusion heatingsystem 24 consists of radio frequency antennas that generate radio wavesto heat the plasma. These produce rotating magnetic fields. The antennasare arranged in an odd-parity arrangement so the sign of the rotatingmagnetic fields flips across the centerline of the field reversedconfiguration plasma. To start the fusion engine, Deuterium may beheated to about 50 kEV and Helium-3 may be heated to about 100 kEV.Roughly 1 MW for 10 seconds should be produced for the engine to start.

Certain types of nuclear fusion reactors produce power from theirradio-frequency heating systems 30 by running it in reverse. In thismode, the antennas absorb radio frequency (RF) energy produced by themotion of the charged particles in the magnetic fields in the reactor.This is known as synchrotron radiation. The radio frequency waves induceelectric currents in the antennas that can be used for poweringelectrical machinery. This is similar to the operation of monostaticradar. This can produce electricity once the fusion reaction isstarting.

Waste heat 26 from bremsstrahlung and other sources is removed usingheat exchangers 28. This heat goes to the heat engine 32. Electricity isgenerated by the heat engine 32.

Limited surge power, if required, may be provided by supercapacitors orflywheels, 34. These devices store large amounts of power for shortdurations and can discharge rapidly. This may only be needed if a veryshort duration pulse was needed during the startup process.

The heat engine 32 drives an electric generator 36 which provides powerto electrolysis unit 22. Oxygen 38 from the electrolysis unit 22 flowsto the oxygen storage tank 14. Hydrogen 40 from the electrolysis unit 22flows to the hydrogen storage tank 12.

FIG. 2 shows a flow diagram of the operation.

The shutdown in a fusion engines is detected, step 42.

If there are other engines, they are checked to see if they areoperating, 44. If one is operating it is used to startup the shutdownfusion engine, step 46.

If none are operating, the valves for the hydrogen and oxygen tanks areopened, step 48. Utilizing well-known fuel cell techniques, the hydrogenand oxygen fuel is combined in the combustion chamber to produce energywhich is ultimately used to produce electrical power, for example atheat engine 32.

Power from the combustion is used to start up the engine, step 50. Thecombustion of the fuel and oxidizer produces heat. This is used to heatthe working fluid in the heat engine that drives an electric generator.Many heat engines, such as Striling or Brayton cycle can be used forthis purpose. The electric generator can also be of many types includingDC or AC generators.

Engine operation is observed, 52. If the engine is operating, the powerfrom the electric generator 36 is sent to the electrolysis unit to beingthe process to recover fuel, step 54.

The system goes into standby when the fuel is recovered and the fusionengine is operating, step 56.

Examples of fusion powered engines for use in space may be found inInternational Application No. PCT/US2013/040520 filed on May 10, 2013and International Patent Application No. PCT/US2013/033767 filed on Mar.25, 2013, the disclosures of which are incorporated by reference as iffully disclosed herein.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

The invention claimed is:
 1. A method for providing power for startup of a nuclear fusion reactor, the method comprising: generating, in a startup system for a field-reversed configuration (FRC) fusion reactor, heat energy by combusting a fuel in one or more combustion chambers, wherein the combusting of the fuel produces a combustion product; generating, by a heat engine, a first electrical power from the heat energy of the startup system; heating, by one or more radio frequency antennas of the FRC fusion reactor, plasma inside the FRC fusion reactor to a temperature of at least 50 kiloelectronvolts to start a fusion nuclear reaction using the first electrical power; generating, by the heat engine, a second electrical power from heat generated by the fusion nuclear reaction; and producing, using the second electrical power, the fuel for the startup system from the combustion product.
 2. The method of claim 1 in which the fuel is a combination of a hydrogen isotope and oxygen.
 3. The method of claim 2 in which the hydrogen isotope is deuterium.
 4. The method of claim 1 further comprising: storing a portion of the second electrical power in a power storage device.
 5. The method of claim 4 in which said power storage device is one or more supercapacitors.
 6. The method of claim 4 in which said power storage device is one or more flywheels.
 7. The method of claim 1, wherein the FRC fusion reactor comprises a plurality of superconducting flux coils around a reactor chamber in which an induced current is generated in response to an odd-parity rotating magnetic field, wherein the induced current generates a magnetic confinement field that magnetically confines the plasma.
 8. The method of claim 1, further comprising: stopping the startup system from generating the first electrical power after the fusion reaction is started.
 9. The method of claim 8, further comprising: stopping the fusion reaction after a period of time.
 10. A nuclear fusion reactor system comprising: a startup system for a field-reversed configuration (FRC) fusion reactor that generates heat energy by combusting a fuel in one or more combustion chambers, wherein the combusting of the fuel produces a combustion product; a heat engine that generates a first electrical power from the heat energy of the startup system and generates a second electrical power from the heat energy generated by the FRC fusion reactor; one or more radio frequency antennas that heat plasma inside the FRC fusion reactor to a temperature of at least 50 kiloelectronvolts to start a fusion nuclear reaction using the first electrical power; and an electrolysis unit that converts the combustion product into the fuel for the startup system.
 11. The system according to claim 10, wherein the fuel is a combination of a hydrogen isotope and oxygen.
 12. The system according to claim 11, wherein the hydrogen isotope is deuterium.
 13. The system according to claim 10, wherein the FRC fusion reactor comprises a plurality of superconducting flux coils around a reactor chamber in which an induced current is generated in response to an odd-parity rotating magnetic field, wherein the induced current generates a magnetic confinement field that magnetically confines the plasma.
 14. The system according to claim 10, wherein the startup system stops generating the first electrical power after the fusion reaction is started.
 15. The system according to claim 14, wherein the fusion reaction is stopped after a period of time. 